CN106358301B - Random access mechanism for link budget limited devices - Google Patents

Abstract

A random access mechanism for a link budget limited device is disclosed, comprising: broadcasting a Physical Random Access Channel (PRACH) configuration index (PCI) reserved for Link Budget Limited (LBL) devices; configuring the LBL device to use the PCI offset from the normal PCI of the current cell; configuring LBL equipment to send PRACH messages by using a substitute subframe set different from a conventionally defined subframe set; when the conventional PRACH configuration specifies an even frame, LBL equipment is configured to send a PRACH message on the odd frame; configuring the LBL device to generate and use additional PRACH preambles that are not used by non-LBL devices; configuring the LBL equipment to use the B group lead code, and configuring the non-LBL equipment to use the A group lead code; and boosting power of the random access response message after the Nth random access failure by using the preamble conforming to the LBL reservation mode of the preamble.

Description

Random access mechanism for link budget constrained devices

technical field

The present application relates generally to wireless communications, and more particularly, to mechanisms capable of enhancing random access procedures for user equipment devices that are link budget constrained.

Background technique

Wireless user equipment (UE) devices, such as smartphones and tablets, communicate with wireless networks to perform any of a variety of functions, such as phone calls, Internet browsing, email, text messaging, social media updates, use of global positioning System (GPS) navigation, etc.

In LTE, a random access procedure (referred to herein as "RACH") is a procedure for synchronizing user equipment (UE) devices with the network (NW). RACH may be used for: initial access by UE device to NW; handover of UE device from one cell to another cell; RRC re-establishment; uplink and/or downlink data arrival; positioning in RRC connection. RACH is a process that allows a UE to access the NW, synchronize with uplink signals from different UE devices, and obtain orthogonal resources. Therefore, it is important to ensure that RACH messages are successfully delivered.

However, some wireless devices may be Link Budget Limited (LBL) and, therefore, experience difficulty in receiving messages sent by the base stations of the network. Base stations also experience difficulties in receiving messages sent by devices with limited link budgets. A device can be link budget constrained for any of a variety of reasons, for example, if:

The device's antenna system is performing poorly; or

The device's antenna system is designed to be housed in a housing that is too small for optimal transmit and/or receive performance in the frequency band of interest;

The device is located away from the base station; or

An obstacle intervenes between the base station and the device (for example, if the device is located within a building); or

The device's battery power is limited.

Link budget constrained UE devices may have limited RF range in the downlink (receive) direction and/or in the uplink (transmit) direction. Accordingly, there is a need for a mechanism that can enhance the ability of link budget constrained devices and base stations to efficiently exchange messages. In particular, there is a need for a mechanism that can improve the performance of random access procedures for link budget constrained UE devices. if such a mechanism is compatible with (and/or easily scalable from) existing LTE networks, e.g. with minimal or no impact on LTE network capacity, and/or minimal or no impact on LTE physical layer, It is desirable to facilitate ease of implementation of this.

SUMMARY OF THE INVENTION

In one set of embodiments, the base station may be configured to broadcast an alternate PRACH configuration index used by link budget constrained devices, where the alternate PRACH configuration index is different from the cell's regular PRACH configuration index. Link budget constrained devices may be configured to send PRACH messages using the PRACH configuration identified by the alternate index, while non-LBL devices (and/or legacy devices) use the PRACH configuration identified by the regular index. (The surrogate PRACH configuration index may be selected such that the corresponding PRACH configuration has an allowable set of time opportunities for PRACH transmission that is disjoint from the allowable set of regular PRACH configurations.) The base station receives from the LBL device based on the surrogate PRACH configuration PRACH messages are received from non-LBL devices (and/or legacy devices) based on regular PRACH configuration. Therefore, when the base station receives a given PRACH message, the base station can easily determine whether the PRACH message is sent by the LBL device. The replacement index may be signaled by the base station in a new system information block, eg, a new system information block created to signal the RACH parameter(s) to the LBL device.

In one set of embodiments, the LBL device may apply an offset to the cell's regular PRACH configuration index to obtain the LBL-specific index. LBL devices may send PRACH messages using the PRACH configuration identified by the LBL-specific index, while non-LBL devices (and/or legacy devices) use the PRACH configuration identified by the general index. (The offset can be determined such that the PRACH configuration corresponding to the LBL-specific index has an allowable set of temporal opportunities for PRACH transmissions that is disjoint from the allowable set of regular PRACH configurations).

In one set of embodiments, the LBL device may transmit PRACH messages using a modified PRACH configuration having (a) the same allowable set of PRACH formats and frames (SFNs) as the cell's regular PRACH configuration, and (b) A set of allowable subframes that is disjoint from the set of allowable subframes of a regular PRACH configuration. (In the context of LTE, the regular PRACH configuration of a cell is identified by the PRACH configuration index signaled in the system information block of type 2.) Non-LBL devices (and/or legacy devices) may use the regular PRACH configuration to send their PRACH message.

In one set of embodiments, the LBL device may send PRACH messages in odd frames when the regular PRACH configuration of the cell specifies the use of even frames. When sending PRACH messages, non-LBL devices (and/or legacy devices) may obey the regular PRACH configuration, including its restriction on even frames. The base station can thus easily determine whether a given PRACH message corresponds to an LBL device based on whether the PRACH message occurs in an odd-numbered frame or an even-numbered frame.

In one set of embodiments, the LBL device may be configured to generate an extended set of preambles, including additional preambles beyond the normal set of preambles for a cell. The LBL device may select (eg, randomly select) preambles from additional preambles instead of from the regular set. The selected preamble can then be used to send PRACH messages. The base station can thus easily determine whether a given PRACH message corresponds to an LBL device based on whether the included preamble is one of the additional preambles or a regular preamble.

In one set of embodiments, the regular set of PRACH preambles (eg, the regular set defined by existing wireless communication standards such as LTE) may be divided into two groups, Group A and Group B. The base station may configure the use of groups A and B such that non-LBL devices (and/or legacy devices) will select preambles from group A and LBL devices will select preambles from group B. Therefore, when the base station receives a given PRACH message, the base station can easily determine whether the PRACH message is sent by the LBL device by determining the group membership (A or B) of the preamble included in the PRACH message.

The base station may employ any of the above mechanisms to determine whether a given PRACH message was sent by an LBL device. In response to determining that the PRACH message was sent by the LBL device, the base station may employ any of a variety of mechanisms to enhance the likelihood that the random access procedure will successfully complete. For example, the base station may boost the transmit power of the random access response (msg2) sent to the LBL device in response to the received PRACH message, ie, the power boost relative to the power that would be used for the non-LBL device. (In the context of LTE, the random access response may be sent with an RA-RNTI that matches the RA-RNTI of the received PRACH message.) As another example, the base station may employ more complex decoding algorithms and/or receive beamforming to increase the probability of successfully decoding the msg3 of the random access procedure. As yet another example, the base station may boost the power of downlink transmissions to the UE device after the random access procedure is completed. As yet another example, the base station may direct the UE device to use a lower coding rate (more redundancy) and/or a lower modulation order for uplink transmission.

In one set of embodiments, the base station may count the number of failed random access attempts whose preambles are consistent with an LBL-specific pattern of preamble index or preamble index offset. When the count exceeds a given threshold, the base station may start boosting the power of msg2 (ie, the random access response message) for any subsequent random access attempt whose preamble is consistent with the LBL-specific pattern.

The state of a device as a link budget limited can be a permanent condition or a variable condition. For example, some devices may be link budget constrained when located away from the serving base station, but become non-link budget constrained (non-LBL) when located close to the base station. Some devices may be link budget constrained due to design, eg due to having a small size antenna system or having limited power consumption due to smaller battery capacity, etc.

If the UE device is link budget limited (LBL) by design, the UE device may perform any of the currently disclosed methods without determining whether the UE device is link budget limited (or has been classified as being link budget). restricted) explicit steps. For example, whenever one of the currently disclosed methods calls a UE device performing an action (or set of actions) "in response to determining that the UE device is link budget constrained", the UE device that is LBL by design may perform the action (or the set of actions) without the step of determining the LBL state. Knowledge of the LBL state may be built into the software and/or hardware controlling the UE device.

It should be noted that the techniques described herein can be implemented in and/or used with many different types of devices, including but not limited to base stations, access points, cell phones, portable media players, tablet computers, wearable devices , and any of a variety of other computing devices.

This Summary is intended to provide a brief overview of some of the subject matter described in this document. Thus, it will be appreciated that the above-described features are merely examples and should not be considered in any way to narrow the scope or spirit of the subject matter described herein. Other features, aspects, and advantages of the subject matter described herein will become apparent from the following detailed description, drawings, and claims.

Description of drawings

A better understanding of the present subject matter can be obtained when the following detailed description of the embodiments is considered in conjunction with the following drawings.

1A illustrates an example of a wireless communication system in accordance with some embodiments.

Figure IB shows an example of _a base station 102 in communication with _three wireless devices 106i, 1062, and ₁₀₆₃ in accordance with some embodiments.

2 illustrates base station 102 in wireless communication with wireless devices 106A and 106B in accordance with some embodiments.

3 illustrates an example of a wireless communication system in accordance with some embodiments.

Figure 4 shows an example of a base station according to some embodiments.

Figure 5A shows a PRACH preamble sent as part of an uplink frame. (PRACH is an acronym for Physical Random Access Channel.)

Figure 5B shows the structure of a conventional PRACH according to one possible format.

Figure 6 shows the cyclic prefix (CP) and sequence parts of PRACH.

7 illustrates messages that may be exchanged between a user equipment (UE) device and a base station (eg, an eNodeB) as part of a random access procedure.

Figure 8 is a copy of the PRACH configuration listed in Table 5.7.1-2 of 3GPP TS 36.211.

Figure 9 illustrates a method for enabling link budget constrained UE devices to transmit PRACH messages with an alternate PRACH configuration index different from the conventionally signaled PRACH configuration index, according to some embodiments.

Figure 10 illustrates a method of enabling link budget constrained UE devices to transmit PRACH messages with a PRACH configuration index that is offset from a conventionally signaled PRACH configuration index, according to some embodiments.

Figures 11 and 12 illustrate a method of enabling link budget constrained UE devices to transmit using a different allowable set of subframes than those identified by a conventionally signaled PRACH configuration index, according to some embodiments PRACH message.

13 illustrates a method of enabling link budget constrained UE devices to transmit PRACH messages using odd frames when regular PRACH configurations designate even frames as the allowable set of PRACH transmit frames, according to some embodiments.

Figure 14 illustrates a method enabling link budget constrained UE devices to generate additional preambles beyond the conventionally defined set of preambles and transmit PRACH messages with a selected one of the additional preambles, according to some embodiments.

Figure 15 illustrates a method for enabling link budget constrained UE devices to utilize a preamble selected from a subset of the conventionally defined set of preambles when a non-LBL device uses another subset of the conventionally defined set, according to some embodiments. The preamble performs PRACH transmission.

Figure 16A illustrates a method enabling a UE device to signal (to the base station) its status as link budget limited by using a predetermined sequence of PRACH preamble index offsets for consecutive PRACH transmissions, according to some embodiments devices until the current PRACH transmission results in the success of the random access procedure.

Figure 16B illustrates a method enabling a UE device to signal (to the base station) a device whose status is link budget limited by using a sequence of PRACH preamble index offsets, according to some embodiments.

Figure 17 illustrates a method enabling a base station to facilitate random access procedures for link budget constrained devices without knowledge of which PRACH transmitting devices are link budget constrained and which are not, according to some embodiments Completed successfully.

While the features described herein are susceptible to various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings and are described in detail herein. It should be understood, however, that the drawings and detailed description thereof are not intended to be limited to the particular disclosed form, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the subject matter defined by the claims.

Detailed ways

abbreviation

Various acronyms are used throughout this disclosure. Definitions of the most commonly used acronyms that may appear throughout this disclosure are provided below:

BS: base station

DL: Downlink

LBL: Link Budget Limited

LTE: Long Term Evolution

MIB: Master Information Block

NW: Network

PDCCH: Physical Downlink Control Channel

PDSCH: Physical Downlink Shared Channel

PRACH: Physical Random Access Channel

PUCCH: Physical Uplink Control Channel

PUSCH: Physical Uplink Shared Channel

RACH: Random Access Procedure or Random Access Channel

RAR: Random Access Response

RA-RNTI: Random Access - Radio Network Temporary Identifier

RRC: Radio Resource Control

RRC IE: RRC Information Element

RX: receive

SFN: System Frame Number

SIB: System Information Block

SIBn: System Information Block of type n

TTI: send time interval

TX: send

UE: User Equipment

UL: Uplink

UMTS: Universal Mobile Telecommunications System

ZC sequence: Zadoff-Chu sequence

3GPP: 3rd Generation Partnership Project

the term

The following is a glossary of terms used in this disclosure:

storage medium - any of various types of non-transitory memory devices or storage devices. The term "storage medium" is intended to include: installation media, such as CD-ROMs, floppy disks, or tape devices; computer system memory or random access memory, such as DRAM, DDR RAM, SRAM, EDO RAM, Rambus RAM, etc. ; non-volatile memory, such as flash memory, magnetic media (eg hard disk or optical storage); registers or other similar types of memory elements, etc. The storage medium may also include other types of non-transitory memory or combinations thereof. In addition, the storage medium may be located in the first computer system in which the program is executed, or may be located in a different second computer system connected to the first computer system through a network such as the Internet. In the latter example, the second computer system may provide program instructions to the first computer for execution. The term "storage medium" may include two or more storage media that may reside in different locations (eg, in different computer systems connected by a network). A storage medium may store program instructions (eg, embodied as a computer program) executable by one or more processors.

Carrier medium - the storage medium described above as well as physical transmission media such as buses, networks, and/or other physical transmission media that convey signals, such as electrical, electromagnetic or digital signals.

Programmable Hardware Elements - includes various hardware devices including multiple programmable functional blocks connected via programmable interconnects. Examples include FPGAs (Field Programmable Gate Arrays), PLDs (Programmable Logic Devices), FPOAs (Field Programmable Object Arrays), and CPLDs (Complex PLDs). Programmable function blocks can vary from fine-grained (combinatorial logic or look-up tables) to coarse-grained (arithmetic logic units or processor cores). Programmable hardware elements may also be referred to as "reconfigurable logic."

computer system - any of various types of computing or processing systems including personal computer systems (PCs), mainframe computer systems, workstations, network appliances, Internet appliances, A personal digital assistant (PDA), television system, grid computing system, or other device or combination of devices. In general, the term "computer system" may be broadly defined to include any device (or combination of devices) having at least one processor that executes instructions from a storage medium.

User Equipment (UE) (or "UE device") - any of various types of computer system devices, mobile or portable, that perform wireless communications. Examples of UE devices include mobile phones or smart phones (eg iPhone ^™ , Android ^™ based phones, etc.), portable gaming devices (eg Nintendo DS ^™ , PlayStation Portable ^™ , Gameboy Advance ^™ , iPhone ^™ ), laptops, PDAs, portable Internet devices, music players, data storage devices, other handheld devices, wearable devices (eg smart watches), etc. In general, the terms "UE" or "UE device" may be broadly defined to include any electronic, computing and/or telecommunication device (or combination of devices) that is easily transported by a user and that is capable of wireless communication.

Base Station - The term "base station" has the full scope of its ordinary meaning and includes at least a wireless communication base station installed at a fixed location and used to communicate as part of a wireless telephone system or radio system.

Processing element - refers to various elements or combinations of elements. Processing elements include, for example, circuits such as ASICs (application specific integrated circuits), portions or circuits of individual processor cores, entire processor cores, individual processors, programmable hardware devices such as field programmable gate arrays (FPGAs), and /or a larger portion of a system that includes multiple processors.

Channel - The medium used to transmit information from a sender (sender) to a receiver. It should be noted that since the properties of the term "channel" can vary from one wireless protocol to another, the term "channel" as used herein may be considered to be used in a manner consistent with the standard using the type of device to which the term refers. In some standards, the channel width may be variable (eg, depending on device capabilities, frequency band conditions, etc.). For example, LTE can support scalable channel bandwidths from 1.4MHz to 20MHz. In contrast, WLAN channels may be 22 MHz wide, while Bluetooth channels may be 1 MHz wide. Other protocols and standards may include different definitions of channels. Furthermore, some standards may define and use multiple types of channels, eg, different channels for uplink or downlink and/or different channels for different purposes such as data, control information, and the like.

Frequency Band - The term "frequency band" has the full scope of its ordinary meaning and includes at least a portion of the frequency spectrum (eg, radio frequency spectrum) in which a channel is used or reserved for the same purpose.

Link Budget Constrained - includes the full scope of its ordinary meaning, and at least includes devices that exhibit limited communication capabilities or limited communication capabilities relative to devices that are not link budget constrained, or for which Radio Access Technology (RAT) standards have been developed Power characteristics of a wireless device (UE). UEs with limited link budgets may experience relatively limited receive and/or transmit capabilities, which may be due to one or more factors such as device design, device size, battery size, antenna size or design, transmit power, receive power, current transmission medium conditions, and/or other factors. Such devices may be referred to herein as "link budget constrained" (or "link budget constrained") devices. A device may be inherently link budget constrained due to its size, battery level and/or transmit/receive power. For example, a smart watch communicating with a base station via LTE or LTE-A may be inherently link budget constrained due to its reduced transmit/receive power and/or reduced antenna size. Alternatively, the device may not be inherently link budget constrained, eg, may have sufficient size, battery power and/or transmit/receive power for normal communication via LTE or LTE-A, but due to current communication conditions (eg, smartphone at the edge of a cell) etc. may be temporarily link budget constrained. It should be noted that the term "link budget constrained" includes or encompasses power constraints, and thus a power constrained device may be considered a link budget constrained device.

Automatically - means that an action or operation is performed by a computer system (eg, software executed by a computer system) or device (eg, a circuit system, programmable hardware element, ASIC, etc.) without the need to directly specify or perform the action or operation User input. The term "automatically" is thus contrasted with an operation performed or specified manually by a user in which the user provides input to perform the operation directly. An automated process may be initiated by input provided by the user, but then actions performed "automatically" are not specified by the user, ie are not performed "manually" (where the user specifies each operation to be performed). For example, a user filling out an electronic form by selecting each field and providing input specifying information (eg, by typing in information, selecting a checkbox, radio, etc.) is filling out the electronic form manually, even though the computer system must respond to the user action to complete the electronic form. Update the table. The form may be automatically filled out by a computer system, wherein the computer system (eg, software executing on the computer system) analyzes the fields of the form and fills in the form without any user input specifying answers to the fields. As indicated above, the user can invoke auto-filling of the form, but do not participate in the actual filling of the form (eg, the user does not manually specify the field's answer, instead the field's answer is auto-completed). This specification provides various examples of operations that are automatically performed in response to actions the user has taken.

Figure 1 - Wireless Communication System

Figure 1A illustrates one embodiment of a wireless communication system. It should be noted that FIG. 1A represents one of many possibilities, and that features of the present disclosure may be implemented in any of a variety of systems, as desired.

As shown, an exemplary wireless communication system includes a base station 102A that communicates via a transmission medium with one or more wireless devices 106A, 106B, etc. through 106N. The wireless device may be user equipment, which may be referred to herein as "user equipment" (UE) or UE equipment. Some wireless devices may be link budget limited (LBL), while other devices may be non-LBL.

Base station 102A may be a basic transceiver station (BTS) or a cell site, and may include hardware that enables wireless communication with UE devices 106A-106N. Base station 102A may also be equipped to communicate with network 100 (eg, a cellular service provider's core network, a telecommunications network such as a public switched telephone network (PSTN), and/or the Internet, among various possibilities). Accordingly, base station 102A may facilitate communication between UE devices 106 and/or between UE devices 106 and network 100 .

The communication area (or coverage area) of the base station 102 may be referred to as a "cell." Base station 102A and UE 106 may be configured to communicate over a transmission medium using any of various radio access technologies (RATs) or wireless communication technologies, such as GSM, UMTS (WCDMA, TDS-CDMA), LTE, LTE-Advanced (LTE-A), HSPA, 3GPP2CDMA2000 (eg, 1xRTT, 1xEV-DO, HRPD, eHRPD), Wi-Fi, WiMAX, etc.

Accordingly, base station 102A and other similar base stations (not shown) operating in accordance with one or more cellular communication technologies may be provided as a network of cells, which may be provided over a wide geographic area via one or more cellular communication technologies UE devices 106A-N and similar devices provide continuous or nearly continuous overlapping services.

Thus, while base station 102 may currently represent a "serving cell" for UE devices 106A-N as shown in FIG. 1A, each UE device 106 may also be capable of The cells provided by the base station) receive the signal, and these cells may be referred to as "neighbor cells". Such cells may also be capable of facilitating communication between user equipments and/or between user equipments and the network 100 .

Figure IB shows an example of _a base station 102 in communication with _three wireless devices 106i, 1062, and ₁₀₆₃ in accordance with some embodiments. _The wireless devices 106i, ₁₀₆₂ , and ₁₀₆₃ may be implemented by any combination of the wireless devices described above and/or below.

It should be noted that, at least in some cases, the UE device 106 may be capable of communicating using a variety of wireless communication technologies. For example, UE 106 may be configured to utilize GSM, UMTS, CDMA2000, WiMAX, LTE, LTE-A, WLAN, Bluetooth, one or more Global Navigation Satellite Systems (GNSS such as GPS or GLONASS), one or more mobile television Two or more of broadcast standards (eg, ATSC-M/H or DVB-H) etc. to communicate. Other combinations of wireless communication standards, including more than two wireless communication technologies, are also possible. Also, in some cases, the UE device 106 may be configured to communicate using only a single wireless communication technology.

FIG. 2 shows a UE device 106 (eg, one of the devices 106A-106N) in communication with the base station 102 . The UE device 106 may have cellular communication capabilities and, as described above, may be, for example, a mobile phone, a handheld device, a media player, a computer, a laptop or tablet device, a wearable device such as a smart watch, or virtually any type of Devices such as wireless devices.

UE device 106 may include a processor configured to execute program instructions stored in memory. The UE device 106 may perform any of the method embodiments described herein by executing such stored instructions. Alternatively, or in addition, the UE device 106 may include programmable hardware elements such as an FPGA (field programmable gate) configured to perform or perform any portion of any method embodiment described herein. array).

In some embodiments, UE device 106 may be configured to communicate using any of a variety of radio access technologies and/or wireless communication protocols. For example, UE device 106 may be configured to communicate using one or more of GSM, UMTS, CDMA2000, LTE, LTE-A, WLAN, Wi-Fi, WiMAX, or GNSS. Other combinations of wireless communication technologies are also possible.

UE device 106 may include one or more antennas for communicating using one or more wireless communication protocols or technologies. In some embodiments, the UE device 106 may be configured to communicate using a single shared radio. A shared radio may be coupled to a single antenna, or may be coupled to multiple antennas (eg, for MIMO) for performing wireless communications. Alternatively, the UE device 106 may include two or more radios. For example, UE 106 may include a shared radio for communicating using LTE or IxRTT (or LTE or GSM), and a separate radio for communicating using each of Wi-Fi and Bluetooth. Other configurations are also possible.

Figure 3 - Example block diagram of UE

FIG. 3 shows one possible block diagram of UE 106 . As shown, UE 106 may include a system on a chip (SOC) 300, which may include parts for various purposes. For example, as shown, SOC 300 may include processor(s) 302 that can execute program instructions for UE 106 and display circuitry 304 that can perform graphics processing and provide display signals to display 340 . The processor(s) 302 may also be coupled to a memory (eg, memory 306, read only memory (ROM) 350, NAND) that may be configured to receive addresses from the processor(s) 302 and translate those addresses into memory (eg, memory 306, read only memory (ROM) 350, NAND A memory management unit (MMU) 305 at a location in flash memory 310). The MMU 305 may be configured to perform memory protection and page table translation or setup. In some embodiments, MMU 305 may be included as part of processor(s) 302 .

UE 106 may also include other circuits or devices, such as display circuitry 304 , radio 330 , connector interface 320 , and/or display 340 .

In the illustrated embodiment, ROM 350 may include a boot program, which may be executed by processor(s) 302 during startup or initialization. As also shown, the SOC 300 may be coupled to various other circuits of the UE 106 . For example, UE 106 may include various types of memory (eg, including NAND flash memory 310), connector interface 320 (eg, for coupling to a computer system), display 340, and wireless communication circuitry (eg, for utilizing LTE, CDMA2000, Bluetooth, WiFi, GPS, etc.).

UE device 106 may include at least one antenna, and in some embodiments multiple antennas, for performing wireless communications with base stations and/or other devices. For example, UE device 106 may use antenna 335 to perform wireless communication. As noted above, the UE may in some embodiments be configured to communicate wirelessly using multiple wireless communication standards.

As described herein, UE 106 may include hardware and software components for implementing any of the UE-related method embodiments described herein.

The processor 302 of the UE device 106 may be configured to implement some or all of the methods described herein, eg, by executing program instructions stored on a storage medium (eg, a non-transitory computer-readable storage medium). In other embodiments, the processor 302 may be configured as a programmable hardware element, such as an FPGA (field programmable gate array), or as an ASIC (application specific integrated circuit).

Figure 4 - Base Station

FIG. 4 shows one embodiment of the base station 102 . It should be noted that the base station of Figure 4 is only one example of a possible base station. As shown, base station 102 may include processor(s) 404 that can execute program instructions for base station 102 . The processor(s) 404 may also be coupled to a memory (eg, memory 460 and read only memory (ROM) 450 ) that may be configured to receive addresses from the processor(s) 404 and translate those addresses into memory memory management unit (MMU) 440 in place of, or coupled to other circuits or devices.

Base station 102 may include at least one network port 470 . The network port 470 may be configured to be coupled to the telephony network and provide a plurality of devices, such as the UE device 106, access to the telephony network as described above.

Network port 470 (or an additional network port) may also or alternatively be configured to couple to a cellular network, eg, a cellular service provider's core network. The core network may provide mobility-related services and/or other services to various devices, such as UE devices 106 . In some cases, network port 470 may be coupled to a telephony network via a core network, and/or the core network may provide a telephony network (eg, between other UE devices served by a cellular service provider).

The base station 102 may include a radio 430 , a communication link 432 and at least one antenna 434 . The base station may be configured to operate as a wireless transceiver, and may also be configured to communicate with UE device 106 via radio 430 , communication link 432 , and at least one antenna 434 . Communication chain 432 may be a receive chain, a transmit chain, or both. Radio 430 may be configured to communicate via various RATs, including but not limited to GSM, UMTS, LTE, WCDMA, CDMA2000, WiMAX, and the like.

The processor(s) 404 of the base station 102 may be configured to implement some or all of the methods described herein, eg, by executing program instructions stored on a storage medium (eg, a non-transitory computer-readable storage medium) . Alternatively, the processor 404 may be configured as a programmable hardware element, such as an FPGA (field programmable gate array), or as an ASIC (application specific integrated circuit), or a combination thereof.

PRACH specification in 3GPP

Figure 5A shows a preamble 500 in a physical random access channel (PRACH) according to existing LTE specifications. The UE device transmits the PRACH preamble in the uplink frame 510 in order to initiate the random access procedure. (The uplink frame includes multiple subframes.) The time offset and frequency offset of the PRACH preamble within the uplink frame may be determined by higher layer signaling.

Figure 5B shows a specific implementation of a PRACH preamble according to existing LTE specifications. By frequency, the PRACH preamble (including guard sub-carriers at the beginning and end) spans 6 RBs = 1.08 MHz. In time, including Cyclic Prefix (CP) and Guard Time (GT), the PRACH preamble spans one uplink subframe.

Formats 0-3 for the PRACH preamble each use a Zadoff-Chu sequence of length 839, while format 4 uses a Zadoff-Chu sequence of length 139.

The PRACH preamble occupies 6 resource blocks (RBs) in the uplink bandwidth (UL BW).

A PRACH subcarrier occupies 1.25kHz, while a normal UL subcarrier occupies 15kHz. The symbols of the Zadoff-Chu sequence are sent on the corresponding PRACH subcarriers.

For the PRACH preamble, Figure 6 shows a cyclic prefix (CP) of duration T _CP and a sequence portion of duration T _SEQ . (The sequence part contains the Zadoff-Chu sequence.) Table 1 below shows the values of T _CP and T _SEQ in different formats of the PRACH preamble.

Table 1: Random access preamble parameters

Overview of the RACH process

The RACH procedure may involve a series of messages sent between the UE and the base station, as shown in FIG. 7 .

In the first message (MSG1), the UE sends a PRACH preamble to the base station (ie eNodeB in LTE parlance). The PRACH preamble may be configured according to one of the formats discussed above or any other desired format.

In response to decoding the first message, the eNodeB sends a second message (MSG2). The second message may be referred to as a random access response (RAR). The PDSCH of the RAR message may include an uplink grant. The uplink grant may identify the uplink resources in the PUSCH for the UE to transmit uplink data.

In response to decoding the second message, the UE may send a third message (MSG3). In the PUSCH of MSG3, the UE may transmit uplink data. The content of the third message may all vary in different contexts, for example, may depend on the purpose for which the RACH procedure has been invoked. For example, the third message may include an RRC request, a scheduling request (SR), and the like.

In response to receiving the third message, the eNodeB may send a fourth message (MSG4), eg, a contention resolution message.

Channels in LTE

LTE uses various channels so that data can be transmitted across the LTE radio interface. These channels are used to separate different types of data and allow them to be transmitted in an orderly manner across the radio access network. The different channels effectively provide an interface to higher layers within the LTE protocol structure and enable ordered and intended separation of data.

There are three categories or types of LTE data channels as follows.

Physical Channels: These are transport channels that carry user data and control messages.

Transport Channel: Transport channel provides information transfer to Medium Access Control (MAC) and higher layers.

Logical Channel: Serves the Medium Access Control (MAC) layer within the LTE protocol structure.

LTE defines multiple physical downlink channels to carry information received from the MAC layer and higher layers. The LTE downlink includes a Physical Downlink Shared Channel (PDSCH) and a Physical Downlink Control Channel (PDCCH). PDSCH is the primary data bearer channel allocated to users on a dynamic and opportunistic basis. The PDCCH carries control information that indicates to the user equipment how resources in the PDSCH are allowed.

LTE random access configuration

In the random access procedure of LTE, there are many possible PRACH configurations. For each cell, the corresponding eNodeB will signal one of the PRACH configurations (by broadcasting the index of the PRACH configuration in SIB2) for use by devices attempting random access in that cell. This PRACH configuration will identify the preamble format and allowable time resources for devices in the cell to use when transmitting PRACH. The allowable time resources may include allowable system frame numbers (SFNs) and allowable subframe numbers (SFNs). Figure 8 shows the PRACH configuration defined in Table 5.7.1-2 of 3GPP TS 36.211. Each PRACH configuration has a corresponding index that identifies its position within the list of PRACH configurations.

LTE random access preamble

In LTE, a UE in a given cell may initiate random access by sending a preamble selected from a set of preambles. (Each UE may randomly select a preamble from a set of preambles). The UE generates the preamble set using the root sequence number provided by the eNodeB in SIB2. For a given cell, the set of preambles can include up to 64 preambles, and the 64 preambles are divided into two groups: group A and group B.

The eNodeB also broadcasts (in SIB2) the following parameters to configure the use of the preamble group:

numberOfRA-Preambles is the number of non-dedicated random access preambles available in the cell;

messageSizeGroupA is the threshold (in bits) for preamble selection;

sizeOfRA-PreamblesGroupA is the size (ie, number) of random access preambles in the A group. These parameters are included in RACH-ConfigCommon. The number of preambles in group B is equal to the difference 'numberOfRA-Preambles'-'sizeOfRA-PreamblesGroupA'.

According to the LTE specification, if the size of the potential UL message to be sent by the UE is greater than "messageSizeGroupA" and the pathloss is less than the pathloss threshold, the UE selects a preamble from group B.

The UE may measure the path loss based on RSCP. (RSCP is short for Reference Signal Code Power.) The network may broadcast the cell reference signal power sent at the eNodeB in a System Information Block (SIB). The UE measures the received cell reference signal power. The difference between the cell reference signal power and the received value is the path loss.

The path loss threshold can be determined based on the following expression:

PathLossThreshold=P _CMAX -preambleInitialReceivedTargetPower-deltaPreambleMsg3-messagePowerOffsetGroupB,

in

_PCMAX is the maximum transmit power of the UE;

preambleInitialReceivedTargetPower is the network expected received power for the first random access attempt (RACH preamble);

deltaPreambleMsg3 is the power offset between the power of the preamble and Msg3, and

messagePowerOffsetGroupB is the power offset for the preambles in group B.

The following is the definition of the RACH-ConfigCommon information element according to LTE:

Random access - UE identity at MSG1 (PRACH message)

In one set of embodiments, link budget constrained devices may be configured to send PRACH messages with a different PRACH configuration than non-LBL devices. (Non-LBL devices may use a conventionally signaled PRACH configuration.) Thus, the base station can determine whether a received PRACH message corresponds to an LBL device based on whether the PRACH message conforms to a different PRACH configuration or a conventionally signaled PRACH configuration. For a device determined to be an LBL, the base station may invoke one or more mechanisms to increase the likelihood that the random access procedure for the LBL device will complete successfully. For example, the base station may boost the transmit power for the LBL device msg2 (ie, the random access response message).

In one embodiment, the eNodeB may broadcast an alternate PRACH configuration index that is different from the regular PRACH configuration index of the current cell for use by devices with limited link budgets. (Alternative PRACH configuration index may also be different from the regular PRACH configuration index of neighboring cells.) When LBL devices send PRACH messages, they may use the PRACH configuration identified by the alternate PRACH configuration index. (The regular PRACH configuration index is signaled in SIB2. However, an alternative PRACH configuration index can be included in a special SIB for LBL UE devices, which is created to broadcast RACH configuration information for LBL devices new SIB.) In contrast, when non-LBL devices send PRACH messages, they use the PRACH configuration corresponding to the regular PRACH configuration index.

In another embodiment, the LBL device may be configured to employ an alternate PRACH configuration index shifted by a predetermined offset from the current cell's regular PRACH configuration index. LBL devices in the cell may send PRACH messages according to the PRACH configuration identified by the alternate PRACH index, while non-LBL devices in the cell may send PRACH messages according to the PRACH configuration identified by the regular PRACH configuration index. Each LBL device may receive the regular PRACH configuration index from the base station (eg, from SIB2) and calculate the replacement index by adding a predetermined offset. The base station can determine whether a given PRACH message corresponds to an LBL device by determining whether the PRACH format, SFN, and subframe number of the PRACH message are consistent with the alternative PRACH configuration or with the legacy PRACH configuration.

In yet another embodiment, the LBL device may use the preamble format and SFN as defined by the conventionally signaled PRACH configuration, but use a different set of allowable subframes than the set of allowable subframes defined by the conventionally signaled PRACH configuration Subframes are allowed. Therefore, LBL devices and non-LBL devices transmit PRACH messages in the same frame, but in different subframes. For example, according to PRACH configuration 6, only subframes 1 and 6 are conventionally allowed for PRACH transmission. (See table in Figure 8). In this case, the eNodeB may allow LBL devices to use subframes 0, 2-5, 7-9 (or any subset of those subframes) for transmission of PRACH messages. One or more subframes available by LBL devices may be broadcast in a special SIB.

In yet another embodiment, if the regular signaled PRACH configuration for a given cell specifies the use of even-numbered SFNs (eg, configurations corresponding to indices 0-2 and 15-18) for PRACH message transmission, the LBL device may instead Odd SFNs are used, but the preamble format and allowed subframes defined by the regular signaled PRACH configuration are respected. As an example, when the regular signaled PRACH configuration index is 2, LBL devices send their PRACH messages in odd frames - in subframe 7, and use preamble format 0.

In one set of embodiments, the set of available preambles in a cell may be extended to include additional preambles beyond the regular set of preambles. Additional preambles may be used by LBL devices to send PRACH messages, while the regular set of preambles are used by non-LBL devices. For example, in one embodiment, the LBL device may generate an extended set of 128 preambles using the root sequence number provided by the eNodeB. The extended set of 128 preambles may include the regular set of 64 preambles and 64 additional preambles. The LBL device may select (eg, randomly select) a preamble from 64 additional preambles. Because LBL devices and non-LBL devices transmit their PRACH messages using disjoint sets of preambles, the base station can easily determine the set membership (regular set or LBL-specific set) of the preambles contained in the PRACH message to determine whether a given PRACH message corresponds to an LBL device. While the above discussion gives an example where the number of additional preambles is 64, it should be understood that this number may take any of a wide variety of values, eg, depending on the expected or average number of LBL devices in the cell. In some embodiments, the number of additional preambles is dynamically configurable, eg, based on system information broadcast by the base station.

In one set of embodiments, at least a subset of the preambles of group B may be reserved for PRACH transmissions (or connection establishment related PRACH transmissions) for link budget constrained devices. (See above discussion of Group A and Group B.) The eNodeB can configure the cells such that the desired number of preambles are allocated to Group B, and the path loss threshold can be relaxed. (The path loss threshold can be relaxed by setting the path loss threshold to a value large enough to ensure that the LBL UE device will be relaxed by using the path loss test of group B or by increasing the likelihood. It should be noted that LBL UE devices typically have more high path loss values for LBL devices). Alternatively or additionally, the eNodeB may set "messageSizeGroupA" such that non-LBL devices will not use the Group B preamble (or use the Group B preamble infrequently).

In some embodiments, the eNodeB may determine whether the received preamble (ie, the preamble of the received PRACH message) belongs to Group A or Group B. If the preamble belongs to group B, the eNodeB may identify the UE device sending the preamble as an LBL device, and send a random access response message to the UE device, thereby granting sufficient uplink resources to the UE device Used for connection establishment, but the granted uplink resources may have a total size smaller than "messageSizeGroupA". Also, after detecting that the preamble belongs to group B, the eNodeB can boost the power of messages (MSG2 and following) to the LBL device.

In one set of embodiments, a method 900 for operating a user equipment (UE) device may be performed as shown in FIG. 9 . (Method 900 may also include any subset of the features, elements, and embodiments described above in connection with Figures 1-8 and below in connection with Figures 10-17.) Method 900 may be performed by link budget constrained UE devices in order to in the random access process. The method may be implemented by a processing agent of the UE device. A processing agent may be implemented by one or more processors executing program instructions, by one or more programmable hardware elements such as an FPGA, by one or more special purpose hardware devices such as an ASIC, or by any combination of the foregoing.

Although method 900 is described below with respect to multiple steps, it should be understood that in various embodiments: one or more of the steps may be omitted; two or more of the steps may be performed at least partially in parallel ; as desired, one or more steps may be added; and steps may be performed in a different order than described.

At 910, the processing agent may receive the index _ILBL that has been broadcast by the base station. The index _ILBL identifies a first configuration for Physical Random Access Channel (PRACH) transmission by UE devices with limited link budget in the cell corresponding to the base station. The index I _LBL is not the same as the index I _NLBL which is also broadcast by the base station, ie the index I _LBL is not equal to the index I _NLBL in terms of numerical value. The index I _NLBL identifies a second configuration for PRACH transmission by non-link budget constrained UE devices (and/or legacy devices) in the cell, wherein the second configuration is different from the first configuration.

At 915, in response to determining that the UE device has been classified as link budget limited, the processing agent may send a PRACH to the base station, wherein the PRACH is sent according to the first configuration. (In contrast, in response to determining, eg, at a later time, that the UE device has been classified as non-link budget constrained, the UE device may perform PRACH transmissions according to the second configuration).

In some embodiments, the base station may be configured to broadcast a first system information block and a second system information block, wherein the first information block includes the index I _LBL and the second system information block includes the index I _NLBL . The link budget constrained UE device may read the first SIB to determine the index _ILBL . More generally, each link budget constrained UE device may recover the index _ILBL from the first SIB. (In contrast, each UE device that is not link budget constrained can recover the index I _NLBL from the second SIB).

In some embodiments, the second system information block is a type 2 system information block, eg, as defined by the LTE standard.

In some embodiments, the first configuration specifies a first set of allowable time opportunities (eg, allowable subframes) for PRACH transmission by link budget constrained UE devices, and the second configuration specifies for A second set of allowable time opportunities for PRACH transmission by non-link budget constrained UE devices, wherein the first set and the second set are disjoint sets.

In some embodiments, the index I _LBL identifies the first configuration from a list of PRACH configurations defined by existing wireless communication standards, and the index I _NLBL identifies the second configuration from the same list. (For example, the list of configurations may be a list of PRACH configurations specified in 3GPP TS36.211). The UE device may store a copy of the list and access the first configuration from the list based on the index _ILBL . When the UE device is not link budget constrained, eg, at a later time, the UE device may access the second configuration from the list based on the index I _NLBL and perform PRACH with the second configuration instead of the first configuration send.

As noted above, the index I _LBL is not the same as the index I _NLBL . In some embodiments, the index _ILBL is also different from one or more additional PRACH configuration indices broadcast by one or more neighboring base stations, respectively, wherein the one or more additional PRACH configuration indices are broadcast for use respectively corresponding to Use by non-link budget constrained UE devices in one or more additional cells of the one or more additional base stations. In some embodiments, each of the plurality of neighboring base stations may be configured to perform the method 900 . The base station may be configured such that each base station selects its index _{ILBL to be different from its index I NLBL and} from the indices _ILBL and I _NLBL sent by other base stations.

In one set of embodiments, a method for operating a base station may be performed as follows. (The method may also include any subset of the features, elements, and embodiments described above in connection with Figures 1-9 and below in connection with Figures 10-17.) The method may be performed by a base station for use in link budget constraints Random access procedure for limited UE devices. The method may be implemented by a processing agent of the base station. A processing agent may be implemented by one or more processors executing program instructions, by one or more programmable hardware elements such as an FPGA, by one or more special purpose hardware devices such as an ASIC, or by any combination of the foregoing. The processing agent may be configured to transmit wireless signals via a transmitter of the base station and receive wireless signals via a receiver of the base station, eg, as variously described above.

Although the method is described below with respect to multiple steps, it should be understood that in various embodiments: one or more of the steps may be omitted; two or more of the steps may be performed at least partially in parallel ; as desired, one or more steps may be added; and steps may be performed in a different order than described.

The processing agent can broadcast the index _ILBL . The index _ILBL identifies a first configuration for Physical Random Access Channel (PRACH) transmission by link budget-constrained UE devices in the cell corresponding to the base station. The index I _LBL is not the same as the index I _NLBL which is also broadcast by the base station, ie the index I _LBL is not equal to the index I _NLBL in terms of numerical values. The index I _NLBL identifies a second configuration for PRACH transmission by non-link budget constrained UE devices (and/or legacy devices) in the cell, wherein the second configuration is different from the first configuration.

The processing agent may receive PRACH, ie PRACH that has been sent by the UE device. The processing agent may determine whether the PRACH has been sent according to the first configuration or according to the second configuration. The first configuration and the second configuration may have different preamble formats, and/or different allowed system frame numbers, and/or different allowed subframe numbers. Any or all of these differences may be used as a basis for determining whether the PRACH has been sent according to the first configuration or according to the second configuration.

In response to determining that the PRACH has been sent according to the first configuration, the processing agent may invoke one or more communication enhancement mechanisms for transmission to and/or reception from the UE device that sent the PRACH. (For example, the processing agent may boost the power of the random access response message, and/or boost the power of downlink traffic transmissions to the UE device.) In contrast, if the processing agent determines that the PRACH has been transmitted according to the second configuration, then The processing agent may not invoke the one or more communication enhancement mechanisms.

In one set of embodiments, a method 1000 for operating a user equipment (UE) device may be performed as shown in FIG. 10 . (Method 1000 may also include any subset of the features, elements, and embodiments described above in connection with Figures 1-9 and below in connection with Figures 11-17.) Method 1000 may be performed by link budget constrained UE devices in order to in the random access process. The method may be implemented by a processing agent of the UE device. A processing agent may be implemented by one or more processors executing program instructions, by one or more programmable hardware elements, by one or more special purpose hardware devices such as ASICs, or by any combination of the foregoing.

Although method 1000 is described below with respect to multiple steps, it should be understood that in various embodiments: one or more of the steps may be omitted; two or more of the steps may be performed at least partially in parallel ; as desired, one or more steps may be added; and steps may be performed in a different order than described.

At 1010, the processing agent can receive a first index that has been broadcast by a base station, wherein the first index identifies a physical random access channel (PRACH) transmission by a non-link budget constrained UE device in a cell of the base station. first configuration. The first index may be the PRACH configuration index conventionally signaled by the eNodeB of LTE. In other words, the first index may be a PRACH configuration index conforming to the LTE wireless communication standard, eg, as defined in 3GPP TS 36.211.

At 1015, the processing agent may add an offset (ie, a non-zero offset) to the first index in order to obtain a second index, wherein the second index identifies a link budget constrained UE device in the cell for processing Second configuration for PRACH transmission. The second configuration is different from the first configuration.

At 1020, in response to determining that the UE device has been classified as link budget constrained, the processing agent may send a PRACH to the base station, wherein the PRACH is sent according to the second configuration. (In contrast, in response to determining, eg, at a later time, that the UE device has been classified as not link budget constrained, the UE device may perform PRACH transmissions according to the first configuration, which is determined by the first configuration. A configuration identified by an index.) In some embodiments, the first configuration specifies a first set of allowable time opportunities (eg, allowable subframes) for PRACH transmissions, and the second configuration specifies for PRACH transmissions The second set of allowable time opportunities for , where the first set and the second set are disjoint sets.

In some embodiments, the base station is configured to broadcast the first index as part of SIB2 (ie, System Information Block of Type 2), as defined by the specification in 3GPP TS 36.331.

In some embodiments, the first index identifies the first configuration from a list of PRACH configurations defined by existing wireless communication standards, and the second index identifies the second configuration from the same list of PRACH configurations. (For example, the list of PRACH configurations may be a list defined by 3GPP TS 36.211.) In some embodiments, the addition of the offset described above is additive modulo N _LIST , where N _LIST is the number of PRACH configurations in the list.

In some embodiments, the method 1000 further comprises: (a) receiving a third index that has been broadcast by the second base station, wherein the third index identifies a target for use by non-link budget recipients in the second cell corresponding to the second base station (b) adding the same offset (that is, the offset of step 1015) to the third index to obtain the fourth index, wherein the fourth index identifies the third index used by the third index The UE device with limited link budget in the second cell performs a fourth configuration of PRACH transmission; and (c) sends a PRACH to the second base station, wherein the PRACH is sent according to the fourth configuration.

In some embodiments, the offset may be used by multiple base stations including the base station.

In some embodiments, method 1000 may be performed by each of a plurality of neighboring base stations. Different base stations may transmit different values of the first index, but use the same offset to determine their respective values of the second index.

In one set of embodiments, a method for operating a base station may be performed as described below. (The method may also include any subset of the features, elements, and embodiments described above in connection with Figures 1-10 and below in connection with Figures 11-17.) The method may be performed by a base station for use in link budget constraints Random access procedure for limited UE devices. The method may be implemented by a processing agent of the base station. A processing agent may be implemented by one or more processors executing program instructions, by one or more programmable hardware elements such as an FPGA, by one or more special purpose hardware devices such as an ASIC, or by any combination of the foregoing. The processing agent may be configured to transmit wireless signals via a transmitter of the base station and receive wireless signals via a receiver of the base station, eg, as variously described above.

Although the method is described below with respect to multiple steps, it should be understood that in various embodiments: one or more of the steps may be omitted; two or more of the steps may be performed at least partially in parallel ; as desired, one or more steps may be added; and steps may be performed in a different order than described.

The processing agent may broadcast an index I _CONV , where the index I _CONV identifies a first physical random access channel (PRACH) transmission for non-link budget constrained UE devices (and/or legacy devices) in the base station's cell. configuration. The index I _CONV may be a PRACH configuration index conventionally signaled by the LTE base station. The non-link budget constrained UE devices and/or legacy UE devices in the cell may receive the index I _CONV and perform PRACH transmission with the first configuration. Conversely, the link budget constrained UE device in the cell can utilize a known distance from the first configuration offset in the list of allowable configurations - ie the distance known to the base station and the link budget constrained UE device - The second configuration to perform PRACH transmission. See eg Figure 8.

After the index I _CONV is broadcast, the processing agent can receive the PRACH, ie the PRACH that has been sent by the UE device.

The processing agent may analyze the PRACH to determine whether it has been sent according to the first configuration or according to the second configuration. The first configuration and the second configuration may have different preamble formats, and/or different allowed system frame numbers, and/or different allowed subframe numbers. Any or all of these differences may be used as a basis for determining whether the PRACH has been sent according to the first configuration or according to the second configuration.

In response to determining that the PRACH has been sent according to the second configuration, the processing agent may invoke one or more communication enhancement mechanisms for transmission to and/or reception from the UE device that sent the PRACH. (For example, the processing agent may boost the power of the random access response message, and/or boost the power of downlink traffic transmission to the UE device.) In contrast, if the processing agent determines that the PRACH has been transmitted according to the first configuration, then The processing agent may not invoke the one or more communication enhancement mechanisms.

In one set of embodiments, a method 1100 for operating a user equipment (UE) device may be performed as shown in FIG. 11 . (Method 1100 may also include any subset of the features, elements, and embodiments described above in connection with Figures 1-10 and below in connection with Figures 12-17.) Method 1100 may be performed by link budget constrained UE devices, in order to facilitate the random access process. The method may be implemented by a processing agent of the UE device. A processing agent may be implemented by one or more processors executing program instructions, by one or more programmable hardware elements, by one or more special purpose hardware devices such as ASICs, or by any combination of the foregoing.

Although the method 1100 is described below with respect to multiple steps, it should be understood that in various embodiments: one or more of the steps may be omitted; two or more of the steps may be performed at least partially in parallel ; as desired, one or more steps may be added; and steps may be performed in a different order than described.

At 1110, the processing agent may receive an index that has been broadcast by the base station, where the index identifies a configuration for transmission of a Physical Random Access Channel (PRACH) with a conventionally defined set of allowable subframes for PRACH transmission. A conventionally defined set may be used for PRACH transmissions by non-link budget constrained UE devices and/or legacy devices in the cell corresponding to the base station. The conventionally defined set may be the set of allowable subframes defined by a wireless communication standard such as LTE. For example, the conventionally defined set may be the set of allowable subframes corresponding to a selected one of the PRACH configurations defined in 3GPP TS 36.211. (See Table 5.7.1-2 of this specification). The above index may be an index to Table 5.7.1-2 of 3GPP TS 36.211.

At 1115, in response to determining that the UE device has been classified as link budget limited, the processing agent may send a PRACH to the base station. PRACH may be sent in subframes from an alternative subset of allowable subframes, where the alternative set is disjoint from the conventionally defined set of allowable subframes. In some embodiments, the UE device may randomly select subframes from the alternative set. An alternate set of allowable subframes may be reserved for use by link budget constrained UE devices. Link budget constrained UE devices may be designed to use an alternative set (rather than the conventionally defined set) when selecting subframes for PRACH transmission.

In some embodiments, the base station is configured to broadcast system information identifying an alternate set of allowable subframes.

The base station may be configured to monitor an alternate set of allowable subframes for PRACH transmissions from link budget constrained UE devices, and to monitor the available subframes for PRACH transmissions from non-link budget constrained UE devices and/or legacy UE devices. A general defined set of allowed subframes. The ability for link budget constrained UE devices to perform PRACH transmissions using allowable subframes that are disjoint from allowable subframes used by non-link budget constrained UE devices and/or legacy UE devices allows the base station to perform PRACH transmissions with lower Receive PRACH transmissions from UE devices with limited link budget(s) and thus decode these PRACH transmissions with a lower probability of error.

In some embodiments, the base station is configured to broadcast the index as part of a type 2 system information block, as defined by the LTE standard.

In some embodiments, the method 1100 may further comprise: in response to determining that the UE device has been classified as not link budget constrained, sending another PRACH to the base station, wherein the other PRACH is in the available subframe from the allowable subframe Sent in subframes of a conventionally defined set.

In some embodiments, the configuration for PRACH transmission also specifies a format for PRACH transmission, eg, one of the PRACH formats defined in 3GPP TS 36.211. The above PRACH (ie, the PRACH of step 1115 ) may be sent according to a specified format.

In some embodiments, the configuration for PRACH transmission also specifies constraints on allowable frames, eg, as shown in FIG. 8 . The above PRACH may be transmitted in frames that conform to the allowable frame constraints.

In one set of embodiments, a method for operating a base station may be performed as follows. (The method may also include any subset of the features, elements and embodiments described above in connection with Figures 1-11 and below in connection with Figures 12-17). The method may be performed by a base station to facilitate random access procedures for UE devices with limited link budgets. The method may be implemented by a processing agent of the base station. A processing agent may be implemented by one or more processors executing program instructions, by one or more programmable hardware elements such as an FPGA, by one or more special purpose hardware devices such as an ASIC, or by any combination of the foregoing. The processing agent may be configured to transmit wireless signals via a transmitter of the base station and receive wireless signals via a receiver of the base station, eg, as variously described above.

Although the method is described below with respect to multiple steps, it should be understood that in various embodiments: one or more of the steps may be omitted; two or more of the steps may be performed at least partially in parallel ; as desired, one or more steps may be added; and steps may be performed in a different order than described.

The processing agent may broadcast an index, where the index identifies a configuration for transmission of a physical random access channel (PRACH). The configuration may have (associated with) a conventionally defined set of allowable subframes for PRACH transmission. A conventionally defined set may be used for PRACH transmissions by non-link budget constrained UE devices (and/or legacy devices) in the cell corresponding to the base station. (The conventionally defined set may be the set of allowable subframes defined by a wireless communication standard such as LTE.) In contrast, link budget constrained UE devices may be configured to utilize available subframes that are disjoint from the conventionally defined set. Alternative sets of subframes are allowed to perform PRACH transmission.

In addition to having a conventionally defined set of allowable subframes, a PRACH configuration may identify preamble formats and specify constraints on allowable frames for PRACH transmission. (See eg Figure 8). When performing PRACH transmissions, link budget constrained UE devices may use the identified preamble format and use frames that conform to the allowable frame constraints.

After the index has been broadcast, the processing agent can receive the PRACH, ie the PRACH that has been sent by the UE device. The processing agent may determine whether the PRACH has been sent in one of the subframes of the alternate set or one of the subframes of the conventional definition set.

In response to determining that the PRACH has been sent in one of the subframes of the alternative set, the processing agent may invoke one or more communication enhancement mechanisms for transmission to and/or reception from the UE device that sent the PRACH. (For example, the processing agent may boost the power of random access response messages, and/or boost the power of downlink traffic transmissions to the UE device.) In contrast, if the processing agent determines that the PRACH is already in one of the subgroups of the conventionally defined set frame, the processing agent may not invoke the one or more communication enhancement mechanisms.

In one set of embodiments, a method 1200 for operating a user equipment (UE) device may be performed as shown in FIG. 12 . (Method 1200 may also include any subset of the features, elements, and embodiments described above in connection with Figures 1-11 and below in connection with Figures 13-17.) Method 1200 may be performed by link budget constrained UE devices in order to in the random access process. The method may be implemented by a processing agent of the UE device. A processing agent may be implemented by one or more processors executing program instructions, by one or more programmable hardware elements, by one or more special purpose hardware devices such as ASICs, or by any combination of the foregoing.

Although method 1200 is described below with respect to multiple steps, it should be understood that in various embodiments: one or more of the steps may be omitted; two or more of the steps may be performed at least partially in parallel ; as desired, one or more steps may be added; and steps may be performed in a different order than described.

At 1210, the processing agent may receive an index that has been broadcast by the base station. The index identifies the first configuration from the list of configurations for Physical Random Access Channel (PRACH) transmission. Each configuration in the list can have:

a corresponding conventionally defined set of allowable subframes for PRACH transmission by non-link budget constrained UE devices (and/or legacy devices) in the cell corresponding to the base station; and

A corresponding alternative set of allowable subframes for PRACH transmission by link budget-constrained UE devices in the cell, wherein the corresponding alternative set is disjoint from the corresponding conventionally defined set.

The configuration list may be stored in the memory of the UE device.

At 1215, in response to determining that the UE device has been classified as link budget limited, the processing agent may send a PRACH to the base station. PRACH may be sent in one of the subframes from the alternative set of allowable subframes corresponding to the index. If the state of the UE device becomes non-link budget limited, the UE device may transmit PRACH in one of the subframes of the conventionally defined set.

In one set of embodiments, a method 1300 for operating a user equipment (UE) device may be performed as shown in FIG. 13 . (Method 1300 may also include any subset of the features, elements, and embodiments described above in connection with Figures 1-12 and below in connection with Figures 14-17.) Method 1300 may be performed by link budget constrained UE devices in order to in the random access process. The method may be implemented by a processing agent of the UE device. A processing agent may be implemented by one or more processors executing program instructions, by one or more programmable hardware elements, by one or more special purpose hardware devices such as ASICs, or by any combination of the foregoing.

Although the method 1300 is described below with respect to multiple steps, it should be understood that in various embodiments: one or more of the steps may be omitted; two or more of the steps may be performed at least partially in parallel ; as desired, one or more steps may be added; and steps may be performed in a different order than described.

At 1310, the processing agent may receive the index that has been broadcast by the base station. The index may identify the configuration used for Physical Random Access Channel (PRACH) transmission. This configuration may specify that PRACH transmissions by non-link budget constrained UE devices (and/or legacy devices) are restricted to even frames and to a conventionally defined set of allowable subframes. (Uplink frames are numbered consecutively, eg, using system frame numbers).

At 1315, in response to determining that the UE device has been classified as link budget constrained, the processing agent may send a PRACH to the base station, where the PRACH is sent in odd frames and in one of the subframes from the conventionally defined set. By using odd-numbered frames, link-budget-constrained UE devices avoid even-numbered frames, which are used for PRACH transmission by non-link-budget-constrained UE devices. This strategy allows the base station to receive PRACH transmissions from link-budget-constrained UE devices without interference from PRACH transmissions from non-LBL UE devices (and/or legacy devices), and, therefore, decode data from the link with a lower probability of error PRACH transmission for budget constrained UE devices. The base station may be configured to monitor even frames for PRACH transmissions from non-LBL UE devices (and/or legacy devices) and odd frames for PRACH transmissions from link budget constrained UE devices.

In some embodiments, the configuration also specifies the format used for PRACH transmission, eg, one of the formats defined in the LTE standard and mentioned in the "Preamble format" column of Table 5.7.1-2 of 3GPP TS 36.211 . (A copy of that table is given in Figure 8.) The transmission of the PRACH to the base station, the transmission step 1315, may be performed according to the format. The index can be interpreted as the PRACH configuration index for the table. Each value of the PRACH configuration index may identify a corresponding PRACH configuration, including one or more of the following: a corresponding preamble format value, a corresponding constraint on the system frame number (eg, a selection of "even" or "any"), and a possible A corresponding conventionally defined set of allowed subframes.

In some embodiments, method 1300 may further comprise: in response to determining that the UE device has been classified as not link budget constrained, sending another PRACH to the base station, wherein the other PRACH is in the even frame and in the Sent in one of the subframes of the defined set.

In some embodiments, the base station is configured to broadcast the index as part of SIB2 (ie, System Information Block of Type 2), as defined by the LTE standard.

In one set of embodiments, a method for operating a base station may be performed as follows. (The method may also include any subset of the features, elements, and embodiments described above in connection with Figures 1-12 and below in connection with Figures 13-17.) The method may be performed by a base station for use in link budgeting Random access procedure for restricted UE devices. The method may be implemented by a processing agent of the base station. A processing agent may be implemented by one or more processors executing program instructions, by one or more programmable hardware elements such as an FPGA, by one or more special purpose hardware devices such as an ASIC, or by any combination of the foregoing. The processing agent may be configured to transmit wireless signals via a transmitter of the base station and receive wireless signals via a receiver of the base station, eg, as variously described above.

Although the method is described below with respect to multiple steps, it should be understood that in various embodiments: one or more of the steps may be omitted; two or more of the steps may be performed at least partially in parallel ; as desired, one or more steps may be added; and steps may be performed in a different order than described.

Processing agents can broadcast indexes. The index may identify a configuration for transmission of a physical random access channel (PRACH). This configuration may specify (or indicate) that PRACH transmissions by non-link budget constrained UE devices (and/or legacy devices) are restricted to even numbered frames and to a conventionally defined set of allowable subframes.

After broadcasting the index, the processing agent can receive the PRACH, ie the PRACH that has been sent by the UE device. The processing agent can determine whether the PRACH has been sent in an even-numbered frame or an odd-numbered frame. (The processing agent may maintain a system frame number that increments from one uplink frame to the next).

In response to determining that the PRACH has been sent in an odd-numbered frame, the processing agent may invoke one or more communication enhancement mechanisms for transmission to and/or reception from the UE device that sent the PRACH. (For example, the processing agent may boost the power of the random access response message, and/or boost the power of downlink traffic transmissions to the UE device.) In contrast, if the processing agent determines that the PRACH has been sent in an even-numbered frame , the processing agent may not invoke the one or more communication enhancement mechanisms.

Background on conventional PRACH sequence collections

In 3GPP TS 36.211, a list of logical root sequence numbers and corresponding physical root sequence numbers is specified for the Physical Random Access Channel (PRACH). See Table 5.7.2-4 of TS 36.211. The eNodeB signals the logical root sequence number in SIB2. Starting from the signaled logical root sequence number, the UE generates a set of 64 Zadoff-Chu sequences based on: the parameter Ncs (also signaled in SIB2); and the physical root sequences respectively corresponding to consecutive logical root sequence numbers No. In particular, the eNodeB generates a first subset of Zadoff-Chu sequences based on the cyclic shift of the first root sequence (corresponding to the first physical root sequence number) until the first root sequence is exhausted, then based on the second root sequence A cyclic shift (corresponding to the second physical root sequence number) generates a second subset of Zadoff-Chu sequences until the second root sequence is exhausted, and so on until 64 sequences have been generated. According to TS 36.211, the root sequence corresponding to the physical root sequence number u is given by:

where the length N _ZC of the root sequence x _u is given by Table 5.7.2.1 of TS 36.211.

Special preamble used to signal the LBL status of the UE device

In one set of embodiments, a method 1400 for operating a user equipment (UE) device may be performed as shown in FIG. 14 . (Method 1400 may also include any subset of the features, elements, and embodiments described above in connection with Figures 1-13 and below in connection with Figures 15-17.) Method 1400 may be performed by link budget constrained UE devices, in order to facilitate the random access process. This method can be implemented by a processing agent. A processing agent may be implemented by one or more processors executing program instructions, by one or more programmable hardware elements, by one or more special purpose hardware devices such as ASICs, or by any combination of the foregoing.

Although method 1400 is described below with respect to multiple steps, it should be understood that in various embodiments: one or more of the steps may be omitted; two or more of the steps may be performed at least partially in parallel ; as desired, one or more steps may be added; and steps may be performed in a different order than described.

At 1410, the processing agent may receive the logical root sequence number that has been broadcast by the base station.

At 1415, the processing agent may generate a set of preambles based on the data including the logical root sequence number. (The data may also include the parameter Ncs described below.) The act of generating the set of preambles may include determining the first physical root sequence number from a conventional mapping of logical root sequence numbers to physical root sequence numbers. (In the context of LTE, the regular mapping may be the mapping defined by Table 5.7.2.1 of 3GPP TS 36.211.) The set of preambles may include:

a first subset of preambles for physical random access channel (PRACH) transmission by non-link budget constrained UE devices; and

A second subset of preambles for PRACH transmission by link budget constrained UE devices, wherein the first subset and the second subset are disjoint subsets.

In some embodiments, the set of preambles may be generated by applying the sequence generation process of 3GPP TS 36.211 section 5.7.2, but extending the process so that more than 64 preambles are generated. For example, the first 64 sync codes may form a first subset, and the remaining preambles may form a second subset.

At 1420, in response to determining that the UE device has been classified as link budget limited, the processing agent may transmit a PRACH to the base station using one of the preambles from the second subset.

In some embodiments, the processing agent may generate only the second subset of preambles. For example, if the UE device is link budget constrained, it may omit the act of generating the first subset of preambles.

The base station can be configured such that whenever it receives a PRACH, the base station can determine whether the preamble contained in the received PRACH belongs to the first subset or the second subset, eg, by targeting the received PRACH to Correlation is performed on the preambles in the first subset and for the preambles in the second subset. The subset membership of the most relevant preamble indicates whether the UE device sending PRACH is link budget constrained. Accordingly, the UE device of method 1400 may signal its link budget limited status to the base station by transmitting PRACH with preambles selected from the second subset, rather than preambles from the first subset. Upon determining that the UE device is link budget constrained, the base station may invoke one or more enhanced mechanisms for improving the reliability of uplink and/or downlink communications with the UE device, such as mechanisms such as: More complex decoding algorithms are employed for decoding uplink transmissions from UE devices; sending downlink transmissions to UE devices with increased power; and so on. (A non-LBL UE device may transmit PRACH with a preamble selected from the first subset. Thus, the base station may recognize that the device is non-link budget constrained.)

In some embodiments, the base station may also be configured to broadcast the logical root sequence number and parameter Ncs as part of the system information broadcast.

In some embodiments, the first subset of preambles is the set of preambles defined by existing LTE specifications.

In some embodiments, the method 1400 may further include, in response to determining that the UE device has been classified as not link budget constrained, transmitting a PRACH to the base station with one of the preambles from the first subset. (When the UE device moves within a cell, when the UE device's battery is depleted over time or replenished while charging, when other objects in the UE device's physical environment change over time, etc., the LBL state of the UE device can vary.)

In some embodiments, the UE device may randomly select the preamble from the second subset of preambles.

In some embodiments, the set of preambles may be generated by: (1) generating a sequence of physical root sequence numbers based on the received logical root sequence number; and (2) sending a message to the physical root sequence number corresponding to the sequence A cyclic shift is applied to the root sequence of . The sequence of physical root sequence numbers may be generated by mapping consecutive logical root sequence numbers to corresponding physical root sequence numbers using conventional mapping, starting from the signaled logical root sequence numbers.

In one set of embodiments, a method for operating a base station may be performed as follows. (The method may also include any subset of the features, elements, and embodiments described above in connection with Figures 1-14 and below in connection with Figures 15-17.) The method may be performed by a base station so that link budgets are constrained The random access process of the UE device. The method may be implemented by a processing agent of the base station. A processing agent may be implemented by one or more processors executing program instructions, by one or more programmable hardware elements such as an FPGA, by one or more special purpose hardware devices such as an ASIC, or by any combination of the foregoing. The processing agent may be configured to transmit wireless signals via a transmitter of the base station and receive wireless signals via a receiver of the base station, eg, as variously described above.

Although the method is described below with respect to multiple steps, it should be understood that in various embodiments: one or more of the steps may be omitted; two or more of the steps may be performed at least partially in parallel ; as desired, one or more steps may be added; and steps may be performed in a different order than described.

The processing agent can broadcast the logical root sequence number. A non-link budget constrained UE device (and/or legacy device) may use the logical root sequence number to generate the first subset of preambles for PRACH transmission, eg, according to a conventionally defined algorithm. In contrast, link budget constrained UE devices may generate a second subset of preambles for PRACH transmission, wherein the second subset is disjoint from the first subset.

After broadcasting the logical root sequence number, the processing agent can receive the PRACH, ie the PRACH that has been sent by the UE device. The processing agent may determine whether the PRACH has been sent with one of the preambles of the first subset or one of the preambles of the second subset.

In response to determining that the PRACH has been sent with one of the preambles of the second subset, the processing agent may invoke one or more communication enhancement mechanisms for transmission to and/or reception from the UE device that sent the PRACH. (For example, the processing agent may boost the power of random access response messages, and/or boost the power of downlink traffic transmissions to the UE device.) On the other hand, if the processing agent determines that the PRACH has utilized one of the first subsets The preamble is sent, the processing agent may not invoke the one or more communication enhancement mechanisms.

In one set of embodiments, a method 1500 for operating a user equipment (UE) device may be performed as shown in FIG. 15 . (Method 1500 may also include any subset of the features, elements, and embodiments described above in connection with Figures 1-14 and below in connection with Figures 16-17.) Method 1500 may be performed by link budget constrained UE devices in order to in the random access process. This method can be implemented by a processing agent. A processing agent may be implemented by one or more processors executing program instructions, by one or more programmable hardware elements, by one or more special purpose hardware devices such as ASICs, or by any combination of the foregoing.

Although the method 1500 is described below with respect to multiple steps, it should be understood that in various embodiments: one or more of the steps may be omitted; two or more of the steps may be performed at least partially in parallel ; as desired, one or more steps may be added; and steps may be performed in a different order than described.

At 1510, the processing agent may receive system information that has been broadcast by the base station. System information can include one or more of the following elements:

logical root sequence number;

The total number of preambles n _TOTAL included in the preamble set, wherein the preamble set includes a first set of preambles and a second set of one or more preambles, wherein the first and second sets are disjoint (as preambles) a subset of the set); and

The number n ₁ of preambles in the first group.

The number n ₁ is positive but less than the number n _TOTAL :

0<n ₁ <n _TOTAL .

At 1515, the processing agent may generate a set of preambles based on the data including the logical root sequence number. The act of generating the set of preambles may include generating a first set of preambles having a size equal to the number n ₁ , and generating a second set of one or more preambles having a size equal to the difference between the number n _TOTAL and the number n ₁ . The first set of preambles may be reserved for Physical Random Access Channel (PRACH) transmissions by non-link budget constrained UE devices (and/or legacy devices). A second set of one or more preambles may be used for PRACH transmissions by link budget constrained UE devices.

At 1520, in response to determining that the UE device has been classified as link budget constrained, the processing agent may transmit a PRACH to the base station with one of the one or more preambles from the second set.

When the base station receives the PRACH, the base station can determine whether the preamble contained in the received PRACH belongs to the first group or the second group, eg, by assigning the received PRACH to the preamble in the first group and to the second group One or more preambles in the group are correlated. The group membership (first group or second group) indicates whether the UE device sending the PRACH is link budget constrained. In response to determining that a given UE device is link budget constrained (based on group membership), the base station may invoke one or more communication enhancement mechanisms to improve reliability of uplink and/or downlink communications with the UE device sex.

In some embodiments, the above-mentioned system information may include a RACH-ConfigCommon information element conforming to the LTE standard. The RACH-ConfigCommon message may include the number n _TOTAL , the number n ₁ and the message size. The base station may be configured to set the message size equal to a value large enough to reduce the number of non-link budget constrained UE devices using preambles from the second set, (or, to reduce the non-link budget the probability that a limited number of UE devices will use the preamble from the second set).

In some embodiments, the system information may include a RACH-ConfigCommon message conforming to the LTE standard. The RACH-ConfigCommon message may include the number n _TOTAL , the number n ₁ and the power offset. The base station may be configured to set the power offset to a value large enough to increase the number of link-budget-constrained UE devices using preambles from the second set, (alternatively, to increase the link-budget-constrained UE device) probability that the UE device will use the preamble from the second set instead of the preamble from the first set).

In some embodiments, the system information may further include the parameter N _CS , wherein the data of step 1515 includes the parameter Ncs.

In some embodiments, the system information may include a RACH-ConfigCommon message conforming to the LTE standard. The RACH-ConfigCommon message may include the number n _TOTAL , the number n ₁ , an indication of the power offset and an indication of the message size threshold. In these embodiments, method 1500 may also include the following. In response to determining that the UE device has been classified as not link budget constrained, the processing agent may perform operations including:

Determining (a) whether the path loss measured by the UE device is less than based in part on the power

The pathloss threshold determined by the offset, and (b) the uplink to be transmitted by the UE device

Whether the size of the link message is greater than the message size threshold;

In response to determining that (a) and (b) are true, selecting a preamble from the first group; and

A PRACH including the selected preamble is sent.

In one set of embodiments, a method for operating a base station may be performed as follows. (The method may also include any subset of the features, elements, and embodiments described above in connection with Figures 1-15 and below in connection with Figures 16-17.) The method may be performed by a base station so that link budgets are constrained The random access process of the UE device. The method may be implemented by a processing agent of the base station. A processing agent may be implemented by one or more processors executing program instructions, by one or more programmable hardware elements such as an FPGA, by one or more special purpose hardware devices such as an ASIC, or by any combination of the foregoing. The processing agent may be configured to transmit wireless signals via a transmitter of the base station and receive wireless signals via a receiver of the base station, eg, as variously described above.

Although the method is described below with respect to multiple steps, it should be understood that in various embodiments: one or more of the steps may be omitted; two or more of the steps may be performed at least partially in parallel ; as desired, one or more steps may be added; and steps may be performed in a different order than described.

Processing agents can broadcast system information. System information can include one or more of the following elements:

logical root sequence number;

the total number of preambles n _TOTAL included in the preamble set, wherein the preamble set includes a first set of preambles and a second set of one or more preambles, wherein the first and second sets are disjoint; and

The number n ₁ of preambles in the first group.

The UE device may generate the set of preambles based on the data including the logical root sequence number. The act of generating the set of preambles may include generating a first set of preambles having a size equal to the number n ₁ , and generating a second set of one or more preambles having a size equal to the difference between the number n _TOTAL and the number n ₁ . The first set of preambles may be reserved for Physical Random Access Channel (PRACH) transmissions by non-link budget constrained UE devices (and/or legacy devices). In contrast, link budget constrained UE devices may be configured to perform PRACH transmissions with a second set of one or more preambles.

After broadcasting the system information, the processing agent can receive the PRACH, ie the PRACH that has been sent by the UE device. The processing agent may determine whether the PRACH includes preambles from the first set or preambles from the second set.

In response to determining that the PRACH includes a preamble from the second set, the processing agent may invoke one or more communication enhancement mechanisms for transmission to and/or reception from a UE device sending the PRACH. (For example, the processing agent may boost the power of the random access response message, and/or boost the power of downlink traffic transmissions to the UE device.) On the other hand, if the processing agent determines that the PRACH includes a preamble from the first group, The processing agent may then not invoke the one or more communication enhancement mechanisms.

Improved reception of random access MSG2 by devices with limited link budget

According to existing LTE specifications, for each random access attempt, the UE may randomly select a preamble from a set of preambles and transmit the selected preamble in msg1 (ie, PRACH message). The PRACH message may be sent to the network (NW) via the base station. The UE then waits for msg2, the so-called random access response message from the base station. Msg2 may be received in the PDCCH and PDSCH of the downlink subframe within a specific time window relative to the time when msg1 was transmitted. If msg2 is not received within this time window, the UE backs off a certain amount of time and randomly selects another preamble from the group and performs another by sending another PRACH message (including the newly selected preamble) A random access attempt.

Link budget constrained UE devices have an increased probability of missing (eg, unsuccessfully decoded) msg2 compared to non-link budget constrained UE devices. If the eNodeB knows that the UE device is link budget constrained, the eNodeB may boost the power of msg2 so that the probability of successful decoding of msg2 by the UE device can be increased. However, in some cases, the base station may not be able to determine whether the UE is link budget constrained according to msg1.

In some embodiments, Link Budget Limited (LBL) devices may operate as follows.

1) The LBL device may randomly select a preamble from the group of preambles as defined by the 3GPP specification, and transmit the preamble in msg1 of the random access procedure. This transmission may be referred to as a first preamble transmission. If msg2 is received within the expected time window after sending msg1, the LBL device may send msg3 of the random access procedure.

2) If the LBL device fails to receive msg2 within the expected time window after sending msg1, another random access attempt may be initiated. In particular, the LBL device may: back off by a certain amount of time; and perform another transmission of msg1 (with the same preamble as the first preamble transmission, or alternatively, with the next preamble in the preamble sequence) . Backoff refers to waiting a certain amount of time before sending. The backoff amount may be defined, for example, relative to the RA (Random Access) window after MSG1 transmission, and may be fixed or random. For example, the backoff amount may be a fixed value for all preamble transmissions after the first transmission and/or for all LBL devices in the cell.

Therefore, the LBL device can repeatedly send msg1 until msg2 is successfully received. Repeated transmissions of msg1 can use the same preamble. Alternatively, the repeated transmission of msg1 may use a sequence of preambles whose pattern is known to the eNodeB. Successive transmissions of msg1 may use successive preambles from the sequence. (Although the first preamble of the sequence may be randomly selected, the relationship between successive preambles of the sequence may be known to the eNodeB).

In some embodiments, the eNodeB may perform the following operations.

1) The eNodeB can count: the number of times the msg1 has been received with the same preamble, and the number of times the corresponding msg2 procedure has failed. In other words, for a given preamble, the eNodeB can count the number of times the eNodeB has performed the following operations:

msg1 is received and msg1 contains the given preamble; and

msg2 is sent, but msg3 is not received from the UE.

2) If the number of times reaches (or, alternatively, exceeds) a threshold N (eg, N=2, 3, 4, 5, or 6), the eNodeB may respond to one or more subsequent instances of msg1 containing the given preamble And boost the power of sending msg2 until msg3 is received from the UE device. For example, the PDCCH and/or PDSCH of msg2 may be boosted in power.

The "same preamble" mentioned above assumes that the LBL type UE uses the same preamble (as the first preamble transmission) for msg1 retransmission. Alternatively, if a LBL type UE uses a preamble sequence for msg1 transmission, the eNodeB may follow the same preamble sequence. Therefore, the eNodeB can count the number of times in which the eNodeB performs the following operations:

msg1 is received and msg1 contains a preamble consistent with the preamble sequence; and

msg2 is sent, but msg3 is not received from the UE.

In some embodiments, the LBL device may be configured to add a special MAC Control Element (CE) in msg3 as an additional MAC PDU header to indicate to the NW that it is link budget limited. When the base station receives msg3, the base station can determine whether the UE sending msg3 is link budget limited by determining whether a special MAC CE exists in msg3.

In one set of embodiments, the LBL device may transmit the first PRACH message with a first preamble randomly selected from a set of available preambles. If the random access attempt corresponding to the previous PRACH message (eg, the first PRACH message) did not complete successfully, the LBL device may send additional PRACH messages. Therefore, the LBL device can send successive PRACH messages until the random access is successfully completed. Successive PRACH messages may have preambles that conform to the sequence of preamble index offsets. (The LBL device may randomly select a sequence of preamble index offsets from a predetermined set of offset sequences. The predetermined set of offset sequences is known to the eNodeB.) Every PRACH message after the first PRACH message Each PRACH message may include a corresponding preamble determined by:

(a) the corresponding index offset from the selected sequence of index offsets; and

(b) Index I ₀ of the first preamble.

For example, the kth PRACH message following the first PRACH message may include a preamble identified by index I ₀ +offset(k), where offset(k) is the kth offset in the selected index offset sequence shift.

In some embodiments, the random selection from the predetermined set may be based on the eNodeB's cell ID, such that LBL devices in different cells will select different index offset sequences from the predetermined set.

The LBL device may use an index offset sequence selected from a predetermined set of offset sequences. In contrast, when a non-LBL device (and/or legacy device) experiences failure with any given random access attempt (eg, due to missing msg2), it may randomly select another preamble from the set of available preambles code, and send another PRACH message based on the randomly selected preamble. Thus, successive PRACH transmissions from non-LBL devices will generally not coincide with any predetermined set of sequences. (The probability that a non-LBL device will randomly select a preamble sequence consistent with any predetermined set of sequences is very low.)

The eNodeB may count the number of failed RACH attempts whose preambles coincide with a given index offset sequence. As the count grows, the probability of a RACH attempt to associate with an LBL device increases. When the eNodeB receives the current PRACH message consistent with the given sequence of index offsets, the eNodeB can determine whether the count has reached (or alternatively, greater than) the threshold N. If so, the eNodeB may transmit the random access response message (ie, random access msg2) with increased power relative to the power (or powers) used for the first N transmissions of msg2. In some embodiments, the first N transmissions may be sent with a given power P0, and any transmissions of _msg2 after the first N transmissions may be sent with a power (or powers ₎ greater than P0. In one embodiment, successive transmissions of msg2 after the Nth transmission are sent with increasing power.

In one set of embodiments, a method 1600 for operating a user equipment (UE) device may be performed as shown in Figure 16A. (Method 1600 may also include any subset of the features, elements, and embodiments described above in conjunction with Figures 1-15 and below in conjunction with Figure 17.) Method 1600 may be performed by link budget constrained UE devices to facilitate randomization access process. This method can be implemented by a processing agent. A processing agent may be implemented by one or more processors executing program instructions, by one or more programmable hardware elements, by one or more special purpose hardware devices such as ASICs, or by any combination of the foregoing.

Although method 1600 is described below with respect to multiple steps, it should be understood that in various embodiments: one or more of the steps may be omitted; two or more of the steps may be performed at least partially in parallel ; as desired, one or more steps may be added; and steps may be performed in a different order than described.

At 1610, the processing agent may perform one or more iterations of the set of operations until a termination condition is fulfilled. The set of operations may include operations 1615 to 1620 described below.

At 1615, the processing agent may generate a preamble for the PRACH message.

At 1620, the processing agent may send a PRACH message to the base station, wherein the PRACH message includes a preamble. The termination condition may be a condition that the UE device successfully receives a Random Access Response (RAR) message in response to the PRACH message.

The one or more preambles in one or more corresponding transmissions of the PRACH message may be generated based on:

A sequence of preamble index offsets that have been configured (or reserved) for

used by link budget constrained UE devices; and

The first preamble generated for the first of one or more transmissions of the PRACH message

The first index of the code.

In some embodiments, method 1600 may further include selecting the sequence of preamble index offsets from a predetermined set of preamble index offset sequences, wherein the predetermined set is configured (or reserved) for link For budget-constrained UE devices.

In some embodiments, the act of selecting from a predetermined set is a random selection based on the cell ID of the base station.

In some embodiments, the UE device is link budget constrained. Link budget constrained UE devices may require more than one iteration of the set of operations to reach the termination condition.

In some embodiments, for each iteration after the first iteration, the set of operations further includes backing off a fixed amount of time before the next transmission of the PRACH message.

In one set of embodiments, a method for operating a base station may be performed as follows. (The method may also include any subset of the features, elements, and embodiments described above in connection with Figures 1-15 and below in connection with Figures 16B-17.) The method may be performed by a base station for use in link budget constraints Random access procedure for limited UE devices. The method may be implemented by a processing agent of the base station. A processing agent may be implemented by one or more processors executing program instructions, by one or more programmable hardware elements such as an FPGA, by one or more special purpose hardware devices such as an ASIC, or by any combination of the foregoing. The processing agent may be configured to transmit wireless signals via a transmitter of the base station and receive wireless signals via a receiver of the base station, eg, as variously described above.

Although the method is described below with respect to multiple steps, it should be understood that in various embodiments: one or more of the steps may be omitted; two or more of the steps may be performed at least partially in parallel ; as desired, one or more steps may be added; and steps may be performed in a different order than described.

The processing agent may receive the current PRACH message, eg, from the UE device in the cell. Link budget limited type UE devices may be configured to repeatedly transmit PRACH messages with preambles conforming to a known pattern until the random access procedure is successfully completed. In contrast, non-LBL type UE devices (and/or legacy devices) may be configured to randomly select a preamble for each transmission of a PRACH message.

The processing agent may increment the failure count in response to determining that the current PRACH message caused a random access failure and that the preamble in the current PRACH message and one or more previous PRACH message preambles are consistent with a pattern of preambles reserved for LBL type UE devices .

In response to determining that the failure count exceeds (or alternatively, reaches) the threshold, the processing agent may invoke one or more communication enhancement mechanisms for transmission to and/or reception from the UE device sending the PRACH. (For example, the processing agent may boost the power of random access response messages, and/or boost the power of downlink traffic transmissions to the UE device.) On the other hand, if the processing agent determines that the failure count is less than or equal to (or alternatively, less than ) threshold, the processing agent may not invoke the one or more communication enhancement mechanisms.

In one set of embodiments, a method 1650 for operating a user equipment (UE) device may be performed as shown in Figure 16B. (Method 1650 may also include any subset of the features, elements, and embodiments described above in connection with FIGS. 1-16A and described below in connection with FIG. 17. Method 1650 may be performed by UE devices with limited link budgets to facilitate random access The method may be implemented by a processing agent of the UE device. The processing agent may be implemented by one or more processors executing program instructions, by one or more programmable hardware elements, by one or more dedicated hardware such as an ASIC The device is either implemented by any combination of the foregoing.

Although the method 1650 is described below with respect to multiple steps, it should be understood that in various embodiments: one or more of the steps may be omitted; two or more of the steps may be performed at least partially in parallel ; as desired, one or more steps may be added; and steps may be performed in a different order than described.

At 1660, in response to determining that a random access response (RAR) message has not been received after the previous PRACH message was sent, the processing agent may perform a set of operations that includes operations 1665 and 1670 described below. (The processing agent may monitor the expected time window for the RAR message, ie the expected time window after the previous PRACH transmission).

At 1665, the processing agent may generate a preamble based, at least in part, on the current offset in the sequence of preamble index offsets, eg, as variously described above. The sequence of preamble index offsets may have been configured (or, may be dedicated) for use by UE devices with limited link budgets.

At 1670, the processing agent may send a current PRACH message including the generated preamble.

In some embodiments, the preamble described above may be generated based on the current offset and the initial index, eg, as variously described above. The initial index may be the index of the initial preamble used in the initial transmission of the PRACH message.

In some embodiments, method 1650 may further comprise selecting the sequence of preamble index offsets from a predetermined set of preamble index offset sequences, wherein the predetermined set has been configured (or reserved) for Used by UE devices with limited link budget.

In some embodiments, the action of selecting from a predetermined set is a random selection based on the cell ID of the base station.

In some embodiments, the sequence of preamble index offsets may be an alternating sequence, ie, alternating between two different offset values.

In some embodiments, the sequence of preamble index offsets may be a cyclic sequence, ie, cyclic through n _CYC offset values, where n _CYC is greater than or equal to 2.

In some embodiments, the sequence of preamble index offsets may be a sequence of non-zero values, or a sequence of positive values, or a sequence that includes two or more non-zero values and one or more zero values.

In some embodiments, the sequence of preamble index offsets may be a sequence of zero values.

In some embodiments, the UE device is link budget constrained.

In some embodiments, the set of operations further includes backing off a fixed amount of time prior to said transmission of the current PRACH message.

In one set of embodiments, a method 1700 for operating a base station device may be performed as shown in FIG. 17 . (Method 1700 may also include any subset of the features, elements, and embodiments described above in connection with Figures 1-16B.) Method 1700 may be performed to facilitate random access by link budget constrained UE devices. The method may be implemented by a processing agent of the base station. A processing agent may be implemented by one or more processors executing program instructions, by one or more programmable hardware elements, by one or more special purpose hardware devices such as ASICs, or by any combination of the foregoing.

Although the method 1700 is described below with respect to multiple steps, it should be understood that in various embodiments: one or more of the steps may be omitted; two or more of the steps may be performed at least partially in parallel ; as desired, one or more steps may be added; and steps may be performed in a different order than described.

At 1710, the processing agent may receive the current PRACH message after having received multiple previous PRACH messages. Previous PRACH message:

(a) a corresponding preamble with a sequence consistent with the preamble index offset, where

This sequence of preamble index offsets is configured (or, dedicated to) for link preamble

counts restricted user equipment (UE) device usage, and

(b) Random access failure has been caused.

The memory of the base station may store a count of previous PRACH messages.

At 1715, in response to receiving the current PRACH message, the processing agent may send a random access response (RAR) message. The power of the transmission of the RAR message may be less than or equal to the first power level if the current value of the count is less than or equal to the threshold N, where N is an integer greater than one. Alternatively, if the current value of the count is greater than the threshold N, the power of said transmission of the RAR message may be greater than the first power level.

In some embodiments, method 1700 may also include incrementing the count in response to determining:

(1) The preamble of the current PRACH message is consistent with the expected preamble, where the preamble

The preamble of the period is based on the preamble index of the first message among the previous PRACH messages

and the next preamble index offset of the sequence of preamble index offsets; and

(2) In response to the RAR message, the third random access message is not received by the base station.

In some embodiments, the predetermined sequence of preamble index offsets is a sequence of zero values.

In some embodiments, a first of the link budget constrained UE devices is configured to randomly select a sequence of preamble index offsets from a predetermined set of preamble index offset sequences, and utilize the selection A given sequence of preamble index offsets generates preambles for successive random access attempts.

Embodiments of the present disclosure may be implemented in any of various forms. For example, some embodiments may be implemented as a computer-implemented method, a computer-readable storage medium, or a computer system. Other embodiments may be implemented using one or more custom designed hardware devices, such as ASICs. Still other embodiments may be implemented using one or more programmable hardware elements such as FPGAs.

In some embodiments, a non-transitory computer-readable storage medium may be configured such that it stores program instructions and/or data that, if executed by a computer system, cause the computer system to perform methods, such as those described herein Any method embodiment, or any combination of method embodiments described herein, or any subset of any method embodiment described herein, or any combination of subsets.

In some embodiments, an apparatus (eg, UE 106 ) may be configured to include a processor (or set of processors) and a storage medium, wherein the storage medium stores program instructions, wherein the processor is configured to read and Execution of program instructions, wherein the program instructions are executable to implement a method, such as any of the various method embodiments described herein (or, any combination of the method embodiments described herein, or any method embodiment described herein any subset of , or any combination of these subsets). A device may be implemented in any of a variety of forms.

While embodiments have been described above in considerable detail, various variations and modifications will become apparent to those skilled in the art once the above disclosure is fully appreciated. The claims are to be construed to cover all such variations and modifications.

Claims (25)

1. A method for operating a user equipment, UE, device, the method comprising:

receiving a first index from a base station, wherein the first index identifies a first configuration for physical random access channel, PRACH, transmission by a link budget limited UE device in a cell corresponding to the base station, wherein the first index is different from a second index from the base station, wherein the second index identifies a second configuration for PRACH transmission by a non-link budget limited UE device in the cell, wherein the first index is further different from one or more additional PRACH configuration indices used by non-link budget limited UE devices in one or more additional cells respectively corresponding to one or more additional base stations, wherein the first configuration specifies a first set of allowable time opportunities for PRACH transmission by the link limited UE device, wherein the second configuration specifies a second set of allowable time opportunities for PRACH transmission by the non-link limited UE device, wherein the first set and the second set are disjoint;

in response to determining that the UE device has been classified as link budget limited, transmitting a PRACH to a base station, wherein the PRACH is transmitted according to a first configuration.

2. The method of claim 1, wherein the first index is received in a first system information block.

3. The method of claim 1, wherein the first index identifies a first configuration from a list of PRACH configurations, wherein the second index identifies a second configuration from the list of PRACH configurations.

4. A method for operating a user equipment, UE, device, the method comprising:

receiving a logical root sequence number that has been broadcast by a base station;

generating a set of preambles based on the data comprising the logical root sequence number, wherein the generating comprises determining a first physical root sequence number from a conventional mapping of logical root sequence numbers to physical root sequence numbers, wherein the set of preambles comprises:

a first subset of preambles for physical random access channel, PRACH, transmission by a non-link budget limited UE device; and

a second subset of preambles for PRACH transmission by the link budget limited UE device, wherein the first subset and the second subset are disjoint subsets;

in response to determining that the UE device has been classified as link budget limited and in response to determining that a random access response, RAR, message has not been received after transmission of a previous PRACH message:

selecting a preamble from the second subset based on a current offset in a sequence of preamble index offsets, wherein the sequence of preamble index offsets is configured for use by the link budget limited UE device; and

and transmitting the PRACH to the base station by using the selected preamble.

5. The method of claim 4, wherein the base station is further configured to broadcast a logical root sequence number and a parameter Ncs as part of the system information broadcast, wherein the data further includes the parameter Ncs.

6. The method of claim 4, wherein the first subset of preambles corresponds to a set of preambles defined by an LTE standard.

7. The method of claim 4, further comprising:

in response to determining that the UE device has been classified as not link budget limited, transmitting a PRACH to the base station with one of the preambles from the first subset.

8. The method of claim 4, wherein the set of preambles is generated by:

generating a sequence of physical root sequence numbers based on the received logical root sequence numbers; and

applying a cyclic shift to a root sequence corresponding to a physical root sequence number of the sequence.

9. A method for operating a user equipment, UE, device, the method comprising:

receiving system information that has been broadcast by a base station, wherein the system information comprises:

a logical root sequence number; and

a RACH-ConfigCommon message compliant with the LTE standard, wherein the RACH-ConfigCommon message includes:

a total number of preambles included in a set of preambles, wherein the set of preambles includes a first set of preambles and a second set of one or more preambles, wherein the first and second sets are disjoint;

a first number of preambles in the first group, wherein the first number is positive but less than the total number; and

a message size, wherein the message size is large enough to reduce a number of non-link budget limited UE devices using preambles from the second group;

generating a set of preambles based on data comprising a logical root sequence number, wherein the generating comprises generating a first set of preambles having a size equal to a first number, and generating a second set of one or more preambles having a size equal to a difference between the total number and the first number, wherein the first set of preambles is reserved for physical random access channel, PRACH, transmissions by non-link budget limited UE devices, wherein the second set of one or more preambles is used for PRACH transmissions by link budget limited UE devices;

in response to determining that the UE device has been classified as link budget limited, transmitting a PRACH to the base station with one of the one or more preambles from the second group.

10. The method of claim 9, wherein system information further includes a parameter Ncs, wherein the data includes the parameter Ncs.

11. The method of claim 9, wherein the RACH-ConfigCommon message further includes an indication of a power offset and an indication of a message size threshold, wherein the method further comprises:

in response to determining that the UE device has been classified as not link budget limited, performing operations comprising:

determining: (a) whether a pathloss measured by the UE device is less than a pathloss threshold determined in part by a power offset, and (b) whether a size of an uplink message to be sent by the UE device is greater than a message size threshold;

in response to determining (a) and (b) are true, selecting a preamble from the first group; and

transmitting the PRACH including the selected preamble.

12. A method for operating a user equipment, UE, device to facilitate random access to a wireless communication network, the method comprising:

in response to determining that a random access response, RAR, message has not been received after sending a previous PRACH message, performing a set of operations comprising:

generating a preamble based at least in part on a current offset in a sequence of preamble index offsets, wherein the sequence has been configured for use by a link budget limited UE device; and

transmitting a current PRACH message including the generated preamble.

13. The method of claim 12, wherein the preamble is generated based on a current offset and an initial index, wherein the initial index is an index of the initial preamble used in an initial transmission of the PRACH message.

14. The method of claim 12, further comprising:

the sequence of preamble index offsets is selected from a predetermined set of preamble index offset sequences, wherein the predetermined set has been configured for use by a link budget limited UE device.

15. The method of claim 14, wherein the selection from a predetermined set is based on a random selection of cell IDs of base stations.

16. The method of claim 12, wherein the sequence of preamble index offsets is a sequence of zero values.

17. The method of claim 12, the set of operations further comprising backing off for a fixed amount of time prior to the sending of a current PRACH message.

18. A method for operating a base station, the method comprising:

receiving a current PRACH message after a plurality of previous PRACH messages have been received, wherein the previous PRACH messages (a) have respective preambles that are consistent with a sequence of preamble index offsets configured for use by a link budget limited user equipment, UE, device and (b) have resulted in a random access failure, wherein a memory of the base station stores a count of the previous PRACH messages;

in response to receiving the current PRACH message, sending a Random Access Response (RAR) message,

wherein the power of the transmission of the RAR message is less than or equal to a first power level if the current value of the count is less than or equal to a threshold N,

wherein the power of the transmission of the RAR message is greater than a first power level if the current value of the count is greater than a threshold N.

19. The method as recited in claim 18, further comprising:

incrementing the count in response to determining:

a preamble of the current message is consistent with an expected preamble based on a preamble index of a first one of the previous PRACH messages and a next preamble index offset of the sequence of preamble index offsets; and

in response to the RAR message, the third random access message is not received by the base station.

20. The method of claim 18, wherein the predetermined sequence of preamble index offsets is a sequence of zero values.

21. The method of claim 18, wherein a first one of the link budget limited UE devices is configured to randomly select a sequence of preamble index offsets from a predetermined set of preamble index offset sequences and generate preambles for successive random access attempts with the selected sequence of preamble index offsets.

22. A user equipment, UE, device, comprising:

a storage medium having program instructions stored thereon; and

a processing element coupled to the storage medium and configured to execute the program instructions to cause the UE to perform the method of any of claims 1-17.

23. A base station, comprising:

a storage medium having program instructions stored thereon; and

a processing element coupled to the storage medium and configured to execute the program instructions to cause the base station to perform the method of any of claims 18 to 21.

24. A non-transitory computer-readable storage medium having stored thereon program instructions that, when executed by a processing element, implement operations of the method of any of claims 1-21.

25. An apparatus for wireless communication, comprising means for performing operations of the method of any of claims 1-21.

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